C#•2w ago

abstract methods inside EF core queries

I'm trying to model my domain as follows (some EF configuration stuff is left out for brevity)

class Contract
{
    public List<PaymentAttempt> PaymentAttempts { get; }
}

abstract class PaymentAttempt // uses tpc
{
    public abstract bool HasPaid(int amount);
}

class BankPaymentAttempt : PaymentAttempt
{
    public string BankAccount { get; set; }
    public int AmountPaid { get; set; }
    
    public bool HasPaid(int amount) => AmountPaid >= amount;
}

class VipUserPaymentAttempt : PaymentAttempt
{
    public bool IsSuperVip { get; set; }

    public bool HasPaid(int amount) => IsSuperVip;
}

class Contract
{
    public List<PaymentAttempt> PaymentAttempts { get; }
}

abstract class PaymentAttempt // uses tpc
{
    public abstract bool HasPaid(int amount);
}

class BankPaymentAttempt : PaymentAttempt
{
    public string BankAccount { get; set; }
    public int AmountPaid { get; set; }
    
    public bool HasPaid(int amount) => AmountPaid >= amount;
}

class VipUserPaymentAttempt : PaymentAttempt
{
    public bool IsSuperVip { get; set; }

    public bool HasPaid(int amount) => IsSuperVip;
}

I am looking to do a query like:

var outstandingBalance = 123;
context.Contracts
    .Where(contract => contract.PaymentAttempts
        .Any(attempt => attempt.HasPaid(outstandingBalance)
    );

var outstandingBalance = 123;
context.Contracts
    .Where(contract => contract.PaymentAttempts
        .Any(attempt => attempt.HasPaid(outstandingBalance)
    );

EF is not able to translate this query unfortunately Is there a method to handle this? I thought about returning expression trees manually but that seems not very easy

11 Replies

Tvde1OP•2w ago

I'm thinking of

class BankPaymentAttempt : PaymentAttempt
{
    public Expression<Func<int, bool>> HasPaid = (int amount) => AmountPaid >= amount;
}

class BankPaymentAttempt : PaymentAttempt
{
    public Expression<Func<int, bool>> HasPaid = (int amount) => AmountPaid >= amount;
}

but how would I use this inside an any? EF.CompileQuery also wouldn't help me in this case I think I'm trying to refrain from making a complex expression tree soup - even though I know that is possible I wish to receive a query which looks like

SELECT * FROM [Contracts]
LEFT JOIN (
    SELECT [pa].[Id], [pa].[ContractId], [e].Property, [e0].OtherProperty CASE
        WHEN [e].[Id] IS NOT NULL THEN N'VipUserPaymentAttempt'
        WHEN [e0].[Id] IS NOT NULL THEN N'BankPaymentAttempt'
    END AS [Discriminator]
    FROM [PaymentAttempt] AS [pa]
    LEFT JOIN [BankPaymentAttempt] AS [e] ON [pa].[Id] = [e].[Id]
    LEFT JOIN [VipUserPaymentAttempt] AS [e0] ON [pa].[Id] = [e0].[Id]
) AS [s] ON [c].[Id] = [s].[ContractId]
WHERE ([e] IS NULL OR [e].Amount > @__input_amount) -- or something

SELECT * FROM [Contracts]
LEFT JOIN (
    SELECT [pa].[Id], [pa].[ContractId], [e].Property, [e0].OtherProperty CASE
        WHEN [e].[Id] IS NOT NULL THEN N'VipUserPaymentAttempt'
        WHEN [e0].[Id] IS NOT NULL THEN N'BankPaymentAttempt'
    END AS [Discriminator]
    FROM [PaymentAttempt] AS [pa]
    LEFT JOIN [BankPaymentAttempt] AS [e] ON [pa].[Id] = [e].[Id]
    LEFT JOIN [VipUserPaymentAttempt] AS [e0] ON [pa].[Id] = [e0].[Id]
) AS [s] ON [c].[Id] = [s].[ContractId]
WHERE ([e] IS NULL OR [e].Amount > @__input_amount) -- or something

Unknown User•2w ago

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Tvde1OP•2w ago

I can use:

var outstandingBalance = 123;
context.Contracts
    .WhereIsPaid(outstandingBalance)
    .ToListAsync();

public static IQueryable<Contract> WhereIsPaid(this IQueryable<Contract> query, int amount)  
{  
    return query.Where(contract => contract.PaymentAttempts.Any(y =>  
        (y as BankPaymentAttempt)!.AmountPaid >= amount ||  
        (y as VipUserPaymentAttempt)!.IsSuperVip)
    );  
}

var outstandingBalance = 123;
context.Contracts
    .WhereIsPaid(outstandingBalance)
    .ToListAsync();

public static IQueryable<Contract> WhereIsPaid(this IQueryable<Contract> query, int amount)  
{  
    return query.Where(contract => contract.PaymentAttempts.Any(y =>  
        (y as BankPaymentAttempt)!.AmountPaid >= amount ||  
        (y as VipUserPaymentAttempt)!.IsSuperVip)
    );  
}

Though this defeats the open-closed principle. I would rather have each class implement their own filter expression

Unknown User•2w ago

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Tvde1OP•2w ago

a predicate is a delegate that is equal to Func<T, bool>..?

Unknown User•2w ago

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Tvde1OP•2w ago

let me try using the Func<T, bool> instead of an expression - but I'm pretty certain EF will refuse to attempt to translate it

Unknown User•2w ago

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Anton•2w ago

you can't translate it ever the closest you can do is having the property return an Expression<Func<...>> the either use a library that will take it into account idk if projectable does this, it might or like you said, construct a tree manually there is no other way and yes, it is quite complicated then you have it run on the client check you queries

Unknown User•2w ago

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Anton•2w ago

as sure as one can be ef core doesn't transform functions to sql it only transforms expression trees

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abstract methods inside EF core queries

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